1. Field of the Invention
The present invention relates to a safety and alarm device for use in recording apparatus utilizing a linear motor.
2. Description of the Prior Art
FIG. 1 shows an example of the recording apparatus in which a carriage CA is reciprocally driven along a guide member Y2 by means of a linear motor. Detection of the print positions and printing speed control are achieved by a non-magnetic optical slit plate OS. The linear motor is provided with a closed magnetic circuit composed of a permanent magnet PM, a magnetic plate Y1 and a magnetic guide member Y2. A coil C wound on a coil bobbin CB slidably mounted on the magnetic guide member Y2 is displaced under the Fleming's left hand law upon receipt of an electric current to drive a carriage CA structured integral with coil bobbin CB. The reciprocating motion of the carriage along the guide member Y2 is achieved by changing over in direction the electric current supplied to the coil winding C. A graduation plate, such as a non-magnetic optical slit plate OS, is fixed at both ends thereof the folded ends Y1T of the guide member Y2 so as to be parallel thereto. The carriage CA is provided with the coil bobbin CB, a printing head such as an ink jet nozzle NP and slit detecting means (not shown) such as a light-emitting diode and a phototransistor. The drive terminals of the coil C and ink jet nozzle NP, and the electrodes of the light-emitting diode and phototransistor are connected to a flexible cable FL of which the other end is connected to a connector (not shown), whereby the displacement of the carriage and the operation of the ink jet nozzle are controlled through the signal lines FLl of flexible cable FL.
The optical slit plate OS is positioned between the light-emitting diode and the phototransistor, and the phototransistor intermittently receives the infrared light from the light-emitting diode through the slits SS of the optical slit plate to detect the speed and position of the carriage CA in the scanning motion, thereby controlling the speed of scanning and the operations of the ink jet nozzle and the paper feeding stepping motor.
The printed characters are in the form of a dot matrix.
In response to a print instruction signal, the carriage CA initiates the displacement, and the carriage position is detected by the timing signals from the optical slit plate OS. In this manner drive signals are supplied to the ink jet nozzle at its determined position to shoot ink droplets therefrom, thereby performing printing on recording paper (not shown).
Upon completion of the printing operation the carriage CA is returned to the initial position (home position HO) in response to drive pulses of an inverted polarity, while the paper feeding is achieved by the stepping motor MO of which rotation is transmitted with reduction through a motor shaft gear (not shown) and gears G1, G2.
The final gear G2 is fixed on the shaft of the platen PL for feeding the paper by a determined amount in the vertical direction. Upon termination of the printing operation the nozzle NP is displaced to its home position HO having a cap KP, which functions to prevent clogging or drying of the ink jet nozzle and meniscus retraction in the nozzle.
In case, however, the reciprocating motion of the carrige CA along the guide member Y2 is hindered by some reason, for example, by the presence of dust or foreign matter, the motor continues to supply current to the coil C on the coil bobbin CB integral with the carriage CA until the motor is turned off, whereby the heat generated by the coil C may cause deformation of the coil bobbin CB or the breakage of the coil C, thus leading to defective carriage drivability or printing failure.